Matt's RV-7 Project

I got my annunciator controller board back from ExpressPCB. Their board layout software is pretty terrible, but the finished product looks okay. If you look closely, you might be able to spot the switch mounting pad I had to grind off because it was too close to the processor reset line. A real board layout tool would have caught that with a design rule check, but of course the crappy free software doesn't have one. Oh well – that turned out to be the only mistake I made (and believe me, nobody is more surprised than I am).

I grabbed a spare D-sub connector and made a little test harness to power the board and test its inputs and outputs.

In keeping with the time-honored traditions of testing out a new PCB design, I soldered the minimal components needed to get the processor running (power supply, oscillator, and the microcontroller itself) and hooked it up to the debugger to see if I could make it blink an LED.

It blinks! This means that the microcontroller is alive and can be programmed. It doesn't look like much, but if a board can get to this stage, then almost everything is working.

Here's the finished product, with voltage dividers, filters, and driver transistors in place. It will be able to sense up to 8 inputs and control up to 6 annunciator lights, depending on how I choose to write the finished firmware. The end goal here is to be able to do a few things with warning lights that are just slightly more sophisticated than simply hooking up a lamp.

I bought a copy of DeltaCad and spent the weekend teaching myself to use it well enough to create a design for my instrument panel. Unfortunately I can't put a picture of it here for reasons not worth going into. But it's pretty cool.

Your humble author apologizes for the lack of blog-updating. Working sixty hour weeks is incompatible with airplane building! Also, the garage is a furnace this month. However, I did manage to sneak in some time this weekend playing with electronics. I'm designing an annunciator light controller for the panel, which has turned out to be a fun way to exercise the very rusty hardware skills I haven't used since I became a full-time software weenie.

I soldered up a little microcontroller board I bought as a cheap mail-order parts kit:

Then I breadboarded a prototype circuit to verify that the basic design was sound. For this part I raided some old boxes of electronic junk I've been hauling around for at least a dozen years. You just never know when you'll need a 10uF cap on a Saturday night!

Then I spent an afternoon routing a little board. When I used to get paid to design PCBs, I had access to some pretty nice CAD tools. Not so much anymore – the free ExpressPCB software is much less capable, but I got the job done eventually. Next time I might try Eagle, but I think that all the free board layout tools pretty much suck in different ways.

I still haven't settled on the actual annunciator lights I want to use, but at least by next week I should have all the parts I need to make a board to control them.